Proton-driven alternating access in a spinster lipid transporter

Area of Science:

• Biochemistry
• Structural Biology
• Membrane Transport

Background:

• Spinster (Spns) lipid transporters are essential for cellular sphingosine-1-phosphate (S1P) transport.
• Spns2 is a key S1P transporter in human endothelial cells, representing a potential therapeutic target for modulating S1P signaling.

Purpose of the Study:

• To identify novel conformational states of the bacterial Hyphomonas neptunium Spns (HnSpns) transporter.
• To elucidate the proton- and substrate-coupled conformational dynamics of HnSpns within lipid membranes.

Main Methods:

• Integrated approach utilizing lipid membranes to study HnSpns.
• Analysis of conserved residues involved in protonation steps and conformational transitions.
• Investigation of a periplasmic salt bridge's role in transporter conformation.

Main Results:

• Identified conserved residues critical for protonation and regulation of conformational changes.
• Demonstrated sequential protonation coordinating transitions in a ligand-dependent alternating access mechanism.
• Revealed a periplasmic salt bridge (Asp60TM2:Arg289TM7) maintaining a closed transporter conformation.

Conclusions:

• Proton-dependent dynamics on the periplasmic side facilitate ligand exchange.
• Understanding HnSpns conformational dynamics provides insights into S1P transport mechanisms.
• Conserved mechanisms highlight potential strategies for targeting Spns transporters.